In wireless communication systems of the prior art, a Mobile Identification Number (MIN) is assigned to each cellular phone, or user, that is present in the system. The MIN is akin to a phone number and is used by the communication system to identify and communicate with the individual user. Unfortunately, when a user changes his or her cellular phone, the MIN often is re-used in the new phone. If the user chooses to leave both the new and the old phones powered-on, then both phones will respond when a network of the communications system pages the user by transmitting a page that identifies the user's MIN. The first phone to respond to the page is then granted access to the network while the second is blocked. Since the new phone and the old phone are equally likely to respond to the page, the old phone may end up blocking the new phone's access to the network.
For example, FIGS. 1 and 2 illustrate an exemplary call setup messaging sequence of the prior art. FIG. 1 is a block diagram of a wireless communication system 100 of the prior art. Communication system 100 includes a first mobile station (MS) 102, a second MS 104, a Base Station (BS) 106 that provides wireless communication services to MSs 102 and 104, and a Mobile Switching Center (MSC) 108 coupled to BS 106. A same MIN is shared by the two mobile stations, that is, MS 102 and MS 104, and is maintained by each MS in a respective memory device of the MS, such as a removable memory device such as a Subscriber Identity Module (SIM). For example, a user may have purchased a new phone, such as MS 104, that the user uses to make calls but keeps an old phone, such as MS 102, to look up stored contact information that the user does not want to, or cannot, transfer to the new phone.
FIG. 2 is a signal flow diagram 200 of an exemplary call setup messaging sequence executed by communication system 100. Signal flow diagram 200 begins when BS 106 receives a call intended for a user of MSs 102 and 104, and more particularly for MS 104, and broadcasts a Page Message 202 that is intended for MS 104. Page Message 202 includes the MIN associated with MS 104, which MIN identifies MS 104 as a target of the page. However, as the MIN is shared among MS 102 and MS 104, MS 102 will also recognize the MIN and believe that it is the target of the page.
When each of MS 102 and MS 104 receives Page Message 202, the MS determines if the MIN included in Page Message 202 matches a MIN stored in the memory device of the MS. When each of MS 102 and MS 104 determines that there is a match, then the MS responds to the Page Message by conveying a Page Response Message 204, 206 to the BS that includes an Electronic Serial Number (ESN) that is uniquely associated with the MS. For example, suppose MS 102 receives page message 202 prior to MS 104. MS 102 determines that there is a match and conveys a Page Response Message 204 to BS 106 that includes an ESN uniquely associated with MS 102. Similarly, when MS 104 receives Page Message 202 and determines that there is a match, MS 104 conveys a Page Response Message 206 to BS 106 that includes an ESN that is uniquely associated with MS 104. However, Page Response Message 206 is conveyed subsequent to the conveyance of Page Response Message 204.
When BS 106 receives Page Response Message 204 from MS 102, MSC 108 validates MS 102 based on the received ESN and the BS transmits an acknowledgement (BS ACK Order 208) acknowledging receipt of Page Response Message 204. BS 106 allocates a first forward link traffic channel to MS 102 and transmits a Channel Assignment Message (CAM) 212 that identifies a first Walsh Code associated with the first forward link traffic channel and that further identifies MS 104 by including the MIN associated with MS 104. In a Code Division Multiple Access (CDMA) communication system, a forward link traffic channel is defined by multiple spreading codes, including a Walsh Code and a long code that is based on a long code mask corresponding to the ESN of the MS that is allocated the channel.
Similarly, when BS 106 receives Page Response Message 206 from MS 104, MSC 108 validates MS 104 based on the received ESN and BS 106 transmits an acknowledgement (BS ACK Order 210) acknowledging receipt of Page Response Message 206. BS 106 allocates a second forward link traffic channel to MS 104 and transmits a CAM 214 that identifies a second Walsh Code associated with the second forward link traffic channel and that further identifies MS 104 by including the MIN associated with MS 104. However, CAM 214 is transmitted subsequent to the transmission of CAM 212.
Both MS 102 and MS 104 receive CAM 212. Each of MS 102 and MS 104 then determines that it is the intended recipient of the CAM by matching the MIN included in the CAM to the MIN maintained by the MS. Upon determining that there is a match, each MS then tunes to the forward link traffic channel identified in CAM 212, that is, the first forward link traffic channel, based on the first Walsh Code identified in the CAM and the long code based on the MS's ESN. As only MS 102 is aware of the correct ESN, and therefore the correct long code mask, associated with the first Walsh Code and the first forward link traffic channel, only MS 102 can successfully despread the identified forward link traffic channel. MS 102 then performs traffic channel initialization procedures 216 with BS 106, the forward link traffic channel is established between MS 102 and the BS, and MS 102 performs remaining signaling 218 for the setup of the call with the BS via the established traffic channel.
Meanwhile, MS 104 is unable to demodulate the first forward link traffic channel because MS 104 despreads first forward link traffic channel the using a long code based on a wrong ESN. However, MS 104 also misses CAM 214 because the MS has ceased listening for a CAM after receiving CAM 212. When MS 104 fails to arrive on the second forward link traffic channel within a predetermined period of time, the second forward link traffic channel is released and the attempt to set up a call with MS 104 is deemed unsuccessful. As a result, the call is set up with the old phone, that is, MS 102, but is not set up with the new phone, that is, MS 104.
Therefore, a need exists for a method and apparatus that reduces a likelihood that a call is set up with a wrong phone when a sharing of a MIN is permitted in a wireless communication system.